YANMAR - Inner Diaphragm Securing Band 

Part Number - 196420-02730

Fits To - SDe7, SDe15, SDe10, SDE10, SDE15, SDE7 SD20, SD31, SD30 SD20, SD20A-S, SD20B-S, SD20C-S SD25 SD40, SD40-4T, SD50-4T, SD50

You may wish to look at the following parts 

Secondary Diaphragm Outer Securing Band - 196420-02740

Sealing Diaphragm A - SD20,25,30,40,50 - 196420-02712

Diaphragm B - 196420-02722

Outer Seal - Flexible Rubber Fairing -SDe7-15 SD15-25 - 196420-02551